PRB-2

This research examined the effects of different probiotic dosages on three-month-old Guiqian semi-fine wool ram lambs (initial weight: 18.57 ± 0.96 kg). The lambs were randomly assigned to four dietary treatments: a control group (CON) received a standard basal diet, while three experimental groups, PRB1, PRB2, and PRB3, were supplemented with 1,000 mg/kg DMI, 2,000 mg/kg DMI, and 3,000 mg/kg DMI, respectively, of a probiotics blend (containing Bacillus subtilis and Bacillus licheniformis, each ≥ 1 × 10⁸ CFU/g) over a 60-day period. The findings revealed that probiotics supplementation markedly improved final body weight and average daily gain (ADG), with the PRB2 group showing the most pronounced increase (P < 0.01). Compared with control lambs, probiotic-fed lambs presented significantly elevated serum Ig G and Ig A levels and reduced levels of the proinflammatory markers IL-6 and TNF-α (P < 0.05). The PRB2 group also presented increased Ig M, IL-10, and IL-1β concentrations (P < 0.05). Antioxidant profiling revealed that PRB1 lambs presented increased serum GSH-Px, T-AOC, and CAT activity, whereas PRB2 lambs presented further improvements in these markers plus elevated T-SOD and reduced MDA content (P < 0.05). Probiotics also modulated rumen ecology, lowering the NH₃-N concentration (P < 0.05) while increasing the total volatile fatty acid (TVFA) content. The PRB2 group notably altered the microbial composition, decreasing Bacteroidota and Verrucomicrobiota while increasing Firmicutes at the phylum level (P < 0.05). At the genus level, Christensenellaceae_R-7_group and Lachnospiraceae_NK3A20_group increased, whereas Prevotella, Succiniclasticum, Selenomonas, and Eubacterium_coprostanoligenes_group decreased (P < 0.05). The experimental results revealed that the addition of different doses of probiotics to the basal diet improved the growth performance, antioxidant capacity, and immunity of Guiqian semi-fine wool sheep and had a positive effect on the rumen microorganisms of Guiqian semi-fine wool sheep, and the best effect was achieved at the addition level of 2000 mg/kg.